Wireless communication method and wireless communication device

ABSTRACT

A wireless communication method and a wireless communication device. An electronic device for a user equipment in a wireless communication system, including a processing circuit configured to receive, from a base station, channel state information reference signal with a set of reception filters, perform channel estimation on a downlink channel from the base station to the user equipment, select, from the set of reception filters, one or more particular reception filters corresponding to respective channel estimation results that satisfy a first predetermined condition, and signal, from the user equipment to the base station, sounding reference signal with one or more particular transmission filters, wherein the one or more particular transmission filters and one or more particular reception filters are reciprocal respectively.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.17/336,318, filed Jun. 2, 2021, which is a continuation of U.S.application Ser. No. 16/822,034, filed Mar. 18, 2020 (now U.S. Pat. No.11,057,245), which is a continuation of U.S. application Ser. No.16/075,509, filed Aug. 3, 2018 (now U.S. Pat. No. 10,637,688), which isbased on PCT filing PCT/CN2017/071252, filed Jan. 16, 2017, which claimspriority to CN 201610081338.3, filed Feb. 5, 2016, the entire contentsof each of which are incorporated herein by reference.

TECHNICAL FIELD

The present application relates to a wireless communication method and awireless communication device, and more particularly to a wirelesscommunication method and a wireless communication device for frequencydivision duplex (FDD) millimeter wave communication.

BACKGROUND

Recently, Millimeter Wave technology and Massive Multi-InputMulti-Output (MIMO) technology have been considered to be a part of thecritical technology of 5G in the future, and have attracted wideattention from academia and industry. The frequency band of millimeterwave has a large amount of available spectrum resources and can meet theincreasing traffic demand of mobile communications. In addition, due tothe short wavelengths of millimeter waves, according to antennatheories,the antenna size of millimeter wave systems may also be small, so thatit is possible to place hundreds of or even thousands of antennas in asmall space, which is more advantageous for the application oflarge-scale antenna technology in real systems. Further, a beamformingtechnology provided by large-scale antennas can effectively compensatefor the shortcomings of large path fading of millimeter wave channels,and provides the possibility for applying millimeter-wave technology tomobile communications.

SUMMARY

The inventors of the present application have found that in the existingmillimeter wave communication technology as mentioned above, it isnecessary to determine corresponding beamforming parameters for eachuser to perform transmission. However, in a case where both the userequipment and the base station are configured with multiple antennas,the overhead of beam training becomes larger and larger as the number ofantennas and the number of users increase. In addition, in a FDDcommunication system, beam training needs to be performed for uplinkchannels and downlink channels separately, and the overhead of this kindof training is twice that of a TDD communication system. Currently,there is no feasible solution to solve these problems.

Therefore, the present application proposes a new technical solutionaddressing at least one of the above-mentioned problems.

It is one of objects of the present application to provide a technicalsolution for wireless communication.

According to a first aspect of this invention, there is provided anelectronic device for a first communication device in a wirelesscommunication system, comprising: a storage device configured to storean analog codebook for the first communication device, the analogcodebook comprising a plurality of sets of first configurationparameters for a set of phase shifters of the first communicationdevice; and a processing circuit configured to: perform channelestimation on a first channel from a second communication device to thefirst communication device respectively based on the plurality of setsof first configuration parameters and signal transmission from thesecond communication device, select a set of first configurationparameters corresponding to ones of channel estimation results thatsatisfy a first predetermined condition to generate a reduced analogsub-codebook, configure signal transmission from the first communicationdevice to the second communication device based on the analogsub-codebook, to perform channel estimation on a second channel from thefirst communication device to the second communication device.

According to a second aspect of this invention, there is provide a beamtraining method for frequency division duplex (FDD) millimeter wavecommunication, comprising: sending, by a user equipment, an uplinktraining sequence to a base station according to a user terminalcodebook; receiving, by the base station, the uplink training sequenceand calculating channel qualities under multiple combinations betweenweight vectors in the user terminal codebook and weight vectors in abase station terminal codebook; selecting a corresponding channelquality for each weight vector in the base station terminal codebookaccording to the channel qualities to form a first channel quality set:selecting a corresponding channel quality for each weight vector in theuser terminal codebook according to the channel qualities to form asecond channel quality set; selecting a first predetermined number ofchannel qualities from the first channel quality set and generating areduced base station terminal codebook based on the weight vectorscorresponding to the first predetermined number of channel qualities;selecting a second predetermined number of channel qualities from thesecond channel quality set and generating a reduced user equipmentterminal codebook based on the weight vectors corresponding to thesecond predetermined number of channel qualities; and performingdownlink beam training using the reduced base station terminal codebookand the reduced user equipment terminal codebook.

One of advantages of the present disclosure is that the overhead of beamtraining can be reduced.

In addition, according to some embodiments of the present application,it is also possible to increase the average achievable rate of users,thereby improving the performance of the FDD system.

According to some embodiments of the present application, it is alsopossible to further reduce the signaling overhead while maintaining lowoverhead of beam training.

Other features and advantages of the present invention will becomeapparent from the following detailed description of exemplaryembodiments of the present invention with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which constitute a part of thisspecification, illustrate embodiments of the application and, togetherwith the description, serve to explain the principles of the presentdisclosure.

The present disclosure can be more clearly understood from the followingdetailed description with reference to the accompanying drawings, inwhich:

FIG. 1 is a view showing a structure of a base station of the prior art;

FIG. 2 is a view showing a user terminal configured with a singleantenna;

FIG. 3 is a view showing a user terminal configured with multipleantennas;

FIGS. 4a and 4b respectively show views of the configurations of a basestation terminal and a user terminal in a single user system;

FIGS. 5a and 5b respectively show views of the configurations of a basestation terminal and a user terminal under a hybrid precoding frame;

FIGS. 6a and 6b respectively show schematic views of a full-connectionphase-shifting network and a sub-connection phase-shifting network;

FIG. 7a shows a schematic view of an electronic device for acommunication device in a wireless communication system according to anembodiment of the present disclosure;

FIG. 7b shows a schematic view of an electronic device for anothercommunication device in the wireless communication system according toan embodiment of the present disclosure;

FIG. 8 shows a flowchart of performing beam training by using theelectronic device of FIG. 7 in a base station according to an embodimentof the present disclosure;

FIG. 9 shows a flowchart of performing uplink beam training by using anexhaustive search method according to an embodiment of the presentdisclosure;

FIG. 10 shows a flowchart of performing uplink beam training by using asingle feedback search method according to an embodiment of the presentdisclosure;

FIG. 11 shows a flowchart of a method for reducing an analog codebookaccording to an embodiment of the present disclosure;

FIG. 12 shows a flowchart of performing downlink beam training with anexhaustive search scheme;

FIG. 13 shows a flowchart of performing downlink beam training with asingle feedback search scheme;

FIG. 14 shows an example of reducing an analog codebook with anexhaustive search algorithm;

FIG. 15 shows an example of reducing an analog codebook with a singlefeedback search algorithm;

FIGS. 16a and 16b respectively show schematic views of structures of theelectronic devices used for a base station and a user equipmentaccording to another embodiment of the present disclosure;

FIG. 17 shows a diagram of correcting an analog sub-codebook of a basestation according to an embodiment of the present disclosure;

FIG. 18 shows a diagram of correcting an analog sub-codebook of a userequipment according to an embodiment of the present disclosure;

FIG. 19 shows a diagram of correcting an analog sub-codebook of a basestation according to an embodiment of the present disclosure;

FIG. 20 shows a diagram of correcting an analog sub-codebook of a userequipment according to an embodiment of the present application;

FIG. 21 shows a profile of average achievable rate of users versussignal-to-noise ratio according to an embodiment of the presentdisclosure;

FIG. 22 shows a profile of average achievable rate of users versussignal-to-noise ratio according to an embodiment of the presentdisclosure;

FIG. 23 shows an example of a hardware configuration of the electronicdevice according to the present disclosure.

DETAILED DESCRIPTION

Various exemplary embodiments of the present invention will now bedescribed in detail with reference to the accompanying drawings. Noticethat, unless otherwise specified, the relative arrangement, numericalexpressions and numerical values of the components and steps set forthin these embodiments do not limit the scope of the invention.

At the same time, it should be understood that, for ease of description,the dimensions of the various parts shown in the drawings are not drawnto actual proportional relations.

The following description of at least one exemplary embodiment is merelyillustrative in fact and is in no way to be intended as any limitationto the present invention and applications or uses thereof.

Techniques, methods, and apparatus known to those of ordinary skill inthe relevant art may not be discussed in detail, but where appropriate,these techniques, methods, and apparatuses should be considered as partof the specification.

Of all the examples shown and discussed herein, any specific valueshould be construed as merely illustrative and not as a limitation.Thus, other examples of exemplary embodiments may have different values.

It should be notice that similar reference numerals and letters indicatethe like in the following accompanying drawings, and therefore, once anitem is defined in an accompanying drawing, there is no need for furtherdiscussion for it in the subsequent accompanying drawings.

In current wireless communication systems, a digital precodingarchitecture is mainly adopted, in which each antenna is connected to aradio frequency link, and the amplitude values of signals transmitted oneach radio frequency link is adjustable to reduce the interferencebetween multiple-channel data signals carried on the same transmissionresource. For example, FIG. 1 shows the structure of a base station ofthe prior art. As shown in the drawing, under the digital precodingarchitecture, the base station terminal is equipped with M antennas (Mis an integer and M≥1), and each antenna is arranged with acorresponding radio frequency link. A digital precoder obtains K datastreams (K is an integer and K≥1) under the control of a controller, andperforms digital precoding on the K data streams (for example, the Kdata streams are made to flow through a digital preceding matrix with asize of M×K). The coded data is sent to one or more users via radiofrequency links and antennas.

Correspondingly, the user terminal may be configured in various ways.

FIG. 2 shows a user terminal configured with a single antenna. As shownin FIG. 2, the user terminal is provided with a single antenna and acorresponding single radio frequency link. Because the user terminal hasonly one antenna, it can only receive a single data stream. In otherwords in K data streams sent from the M antennas of the base station,only one data stream can be received by the user terminal.

FIG. 3 shows a user terminal provided with multiple antennas. As shownin FIG. 3, the user terminal is configured with N antennas (N is aninteger and N>1). Each antenna transmits the received data to a digitalprecoder through a corresponding radio frequency link. Under the controlof the controller, the digital precoder performs digital precoding onthe received data using for example a digital preceding matrix W with asize of Ku×N (Ku is an integer and Ku≥1), thereby obtainingsingle-channel data (when Ku=1) or multiple channel data (when Ku>1).

For digital preceding matrices used in digital precoders, there areusually two design schemes: codebook based and non-codebook based. Inthe codebook based design scheme, a digital preceding matrix must beselected from a predetermined codebook. While in the non-codebook baseddesign scheme there is no such constraint. The base station terminal andthe user terminal can design the precoding matrix according to ChannelState Information (CSI).

In a millimeter wave communication system, since the implementationcomplexity and cost of a radio link is relatively high, each radiofrequency link is usually used to connect multiple phase shifters andantennas to form a directional beam by using as few as one radio link,thereby achieving an analog beamforming scheme. The main role of theanalog beamforming is to improve the signal-to-noise ratio of userreception.

Millimeter wave communication systems have multiple operating modes,such as point-to-point mode, single user mode, multi-user mode, etc. Thepoint-to-point mode can be used for the backhaul between the basestations (BS), the single user and multi-user modes can be used for thecommunication between a base station and one or more user equipments(UE). In terms of implementation architecture, it may comprise analogbeamforming, full-connection hybrid precoding, sub-link hybrid precodingand the like. Regardless of which architecture is adopted, weightvectors of the base station and user equipment can only be selected froma predefined analog codebook due to the limitation of the deviceconstraints. Beam training refers to the process of selecting theoptimal transmiting/receiving weight vectors from the analog codebook.

FIGS. 4a and 4b respectively show the configurations of a base stationterminal and a user terminal in a single user system. As shown in FIG.4a and FIG. 4b , in the user terminal and the base station terminal,each radio frequency link is connect to a set of phase shifters, andeach phase shifter is then connected to corresponding antennarespectively. Values (e.g., phase values) of a set of the phase shiftersform a weight vector used to transmit an antenna beam in a specificdirection. In some examples, the parameters used to generate a beam arealso referred to as a beam vector. Herein, the weight vector at the basestation terminal is represented as f and the weight vector at the userterminal is represented as w. Since the phase shifter only adjusts thephase of a signal without changing its amplitude, the amplitude value ofeach element in the weight vector is 1. In a millimeter wavecommunication system having such structure, due to the limited number ofradio frequency links, neither the base station terminal nor the userterminal can directly estimate the channel state information. Thus, theconventional analog beamforming scheme uses a codebook based method. Thecodebook is a collection of a set of weight vectors. suppose the basestation terminal codebook is Fc with a size of P (including P weightvectors), the user terminal codebook is We with a size of Q (including Qweight vectors), weight vectors of the base station terminal must beselected from the base station terminal codebook Fc, and weight vectorsof the user terminal must be selected from the user terminal codebookWc.

When millimeter wave communication is performed by the base stationterminal and the user terminal, which weight vector in the codebook isspecifically adopted is determined in advance by beam training. Thecriterion of maximizing signal-to-noise ratio can be used in the beamtraining. Taking the downlink beam training as an example, it can beexpressed by equation (1):

{w_(opt), f_(opt)}=argmax∥w^(T)Hf∥ wherein w ∈ W_(c), f ∈ F_(c)   (1)

In the above equation (1), H represents a channel between the basestation terminal and the user terminal.

The beam training algorithm can use an exhaustive search method, asingle feedback search method or the like. The following descriptionwill take the downlink beam training as an example.

-   1. Exhaustive Search. The exhaustive search algorithm detects all    the possible combinations between weight vectors of the base station    terminal and weight vectors of the user terminal, and the user    terminal measures the channel quality under each pair of weight    vectors, selects an optimal set of weight vectors, and feeds an    index of the optimal weight vector of base station terminal back to    the base station. The exhaustive search mechanism can achieve    optimal performance, but resulting in extremely high complexity    because of the need to detect all the combinations of the weight    vectors.

In order to reduce the complexity of the beam training algorithm, it ispossible to only select a portion of all the combinations between weightvectors of base station terminal and weight vectors of user terminal fordetection. For example, it may be combinations between one weight vectorin the base station terminal codebook and all the weight vectors in theuser terminal codebook, or it may be combinations between one of theweight vectors in the user terminal codebook and all the weight vectorsin the base station terminal codebook. For example, in one embodiment,one of the weight vectors in the user terminal codebook to be combinedwith all the weight vectors in the base station terminal codebook may beselected according to the channel qualities obtained from thecombinations between one of the weight vectors in the base stationterminal codebook and all the weight vectors in the user terminalcodebook. A specific example is a single feedback search.

-   2. Single Feedback Search. In the single feedback search, beam    training is divided into two processes. Downlink is still taken as    an example. Firstly, the base station sends a signal (for example, a    pilot signal) according to each weight vector in the base station    terminal codebook, the user terminal receives the signal with an    omni-directional beam (for example, a weight vector predetermined at    the user terminal wherein only one antenna of the antenna array is    used for reception) and estimates the channel quality corresponding    to each weight vector in the base station terminal codebook, and    then the user terminal selects a weight vector resulting in an    optimal channel quality from the weight vector in the base station    terminal codebook and feeds back its index to the base station.    Then, the base station uses the weight vector selected by the user    terminal fixedly to send signals, and the user terminal selects a    weight vector with the highest channel quality from its codebook as    the weight vector for communicating with the base station (i.e.,    calculating the channel quality obtained from the combinations    between each weight vector in the user terminal codebook and the    fixed weight vector of the base station terminal, and selecting a    combination corresponding to the highest channel quality). Compared    to the exhaustive search mechanism, the complexity of the single    feedback mechanism is greatly reduced, but resulting in a certain    loss of performance at the same time.

The above description is given by taking downlink transmission as anexample. A similar process is performed in the process of uplinktransmission, and the main difference is that the user terminal sendssignals and the base station terminal receives the signals. In addition,the channel quality can be obtained by channel estimation. Channeldirection and channel quality can be obtained by the channel estimation.The result of channel estimation may comprise a Channel QualityIndicator (CQI) and identification information of a corresponding set ofparameters (index of optimal weight vector), and may also comprisemultiple optimal CQIs and identification information of a set ofparameters corresponding to each CQI.

In a multi-user scenario, a millimeter-wave wireless communicationsystem may also use a hybrid precoding architecture. FIGS. 5a and 5brespectively show the configurations of a base station terminal and auser terminal in a hybrid precoding architecture.

As shown in FIG. 5a , a base station terminal using a hybrid precodingarchitecture has a digital precoder and an analog phase-shiftingnetwork. Under the control of a controller, the digital precoder obtainsK data streams as input, and the digital precoder performs digitalprecoding on the K data streams, thereby eliminating interferencebetween different data streams. Then, K radio frequency (RF) linksperform up-converting, amplifying, filtering and other processings onthe data streams precoded by the digital precoder to form RF signals.Typically, each of the k RF links corresponds to a user terminal.

The K RF links are connected to an analog phase-shifting network. Thevalues of phase shifters in the phase-shifting network constitute ananalog beamforming matrix F. In the matrix F, the k^(th) columnindicates a set of values of phase shifters connected to the k^(th) RFlink and is represented as a weight vector f_(k), the weight vectorf_(k) must be selected from a codebook fc of the base station terminal.

For the phase-shifting network, it can be implemented in different ways.FIGS. 6a and 6b respectively show a full-connection phase-shiftingnetwork and a sub-connection phase-shifting network.

As shown in FIG. 6a , in a full-connection phase-shifting network, eachRF link is connected to a set of M phase shifters, so that there are Ksets of phase shifters in the full-connection phase-shifting network,and the total number of phase shifters is K×M. The signals output bycorresponding phase shifter in each set of phase shifters (K signals)eadded by an adder and then provided to a corresponding antenna unit.

As shown in FIG. 6b , in a sub-connection phase-shifting network, theoutput of each RF link is connected to P phase shifters (P is an integerand P≥1), and each phase shifter is connected to an antenna unit. Thatis, in the case where there are K RF links, the number of antennaelements is M=K×P.

FIG. 5b shows the configuration of the user terminal using a hybridprecoding architecture. As shown in FIG. 5b , the user terminal isconfigured with N antennas, Signals received by the antennas areinputted to a RF link after passing through corresponding phaseshifters. The values of the phase shifters constitute a user terminalweight vector w_(k), which can be selected from a user terminal codebookWc. The input signal is filtered, amplified, and down-converted by theRF link to obtain a digital received signal.

In this example, the user terminal has only one RF link. According toactual situations, a design of multiple RF links may also be adopted onthe user terminal.

In the hybrid precoding architecture, beam training is a process ofdetermining weight vectors of the base station terminal and the userterminal. With downlink transmission as an example, the criterion ofmaximizing signal-to-noise ratio can be expressed by equation (2):

{w_(k,opt), f_(k,opt)}=argmax∥w^(T)H_(k)f∥ wherein w ∈ W, f ∈ F   (2)

Where {w_(k,opt), f_(k,opt)} represents the optimal downlink weightvector of the k^(th) user, H_(k) is the downlink channel matrix betweenthe base station and the k^(th) user. The exhaustive search mechanism orsingle feedback search mechanism described above or other multi-userbeam search mechanisms can be used in the beam training.

In a TDD system, uplink and downlink channels have reciprocity, i.e.,H^(ul) _(k) of the uplink channel=H_(k) ^(T), and where T denotes thetransposition of a matrix. Therefore, in a TDD system, a combinationbetween optimal base station terminal weight vector and user terminalweight vector in the uplink channel and a combination between optimalbase station terminal weight vector and user terminal weight vector inthe downlink channel are the same. It is only necessary to perform beamtraining on one of the uplink channel and the downlink channel. However,in a FDD system, since the uplink and downlink channels do not havereciprocity therebetween, it is necessary to perform beam training inthe uplink channel and the downlink channel respectively, thereby thecomplexity of beam training is doubled than that in a TDD system.

The applicant noticed that although the uplink channel and the downlinkchannel in the FDD system are not reciprocal, according to the channelmodel proposed by WINNER, the small-angle fading parameters (such as theantenna arrival angles of the base station terminal and the userterminal) of the uplink channel and the downlink channel are the same.Particularly, the downlink channel matrix H^(DL) and the uplink channelmatrix H^(UL) may be represented by the following equations (3) and (4),respectively:

$\begin{matrix}{H^{DL} = {\sqrt{\frac{MN}{N_{cl}N_{ray}}}{\sum\limits_{i = 1}^{N_{cl}}{\sum\limits_{l = 1}^{N_{ray}}{\alpha_{i,l}e^{j\;\psi_{i,l}^{DL}}{a_{UE}^{DL}\left( {\theta_{i,l}^{UE},\phi_{i,l}^{UE}} \right)}{a_{BS}^{DL}\left( {\theta_{i,l}^{BS},\phi_{i,l}^{BS}} \right)}^{H}}}}}} & (3) \\{H^{UL} = {\sqrt{\frac{MN}{N_{cl}N_{ray}}}{\sum\limits_{i = 1}^{N_{cl}}{\sum\limits_{l = 1}^{N_{ray}}{\alpha_{i,l}e^{j\;\psi_{i,l}^{UL}}{a_{UE}^{UL}\left( {\theta_{i,l}^{BS},\phi_{i,l}^{BS}} \right)}{a_{BS}^{UL}\left( {\theta_{i,l}^{UE},\phi_{i,l}^{UE}} \right)}^{H}}}}}} & (4)\end{matrix}$

In the above equations, N and M represent the numbers of antennasprovided at the user terminal and the base station respectively, N_(cl)is the number of scatterers, N_(ray) is the number of sub-pathscontained in each scatterer, and α_(i,l) represents the channelcoefficient of each sub-path, e is the base of natural logarithms, and jis the imaginary unit, a_(UE) and a_(BS) respectively represent antennaresponse vectors of the user terminal and the base station terminal, thesuperscripts UL and DL represent uplink and downlink channelsrespectively, and θ and φ respectively represent the arrival angle in ahorizontal direction and the arrival angle in a vertical direction. Inaddition, ψ_(i,l) represents a random phase of each sub-path and isindependently and uniformly distributed in [0, 2π]. The form of theantenna response vector is associated with the type of antenna. Forexample, in a case of a Uniform Linear Array (ULA) of antennas, theantenna response vector of base station is:

$\begin{matrix}{{a_{BS}^{UL}(\theta)} = {\frac{1}{\sqrt{M}}\left\lbrack {1,e^{j\frac{2\pi\; d}{\lambda_{UL}}{\sin{(\theta)}}},\ldots\mspace{14mu},e^{{j{({M - 1})}}\frac{2\pi\; d}{\lambda_{UL}}{\sin{(\theta)}}}} \right\rbrack}^{T}} & (5) \\{{a_{BS}^{DL}(\theta)} = {\frac{1}{\sqrt{M}}\left\lbrack {1,e^{j\frac{2\pi\; d}{\lambda_{DL}}{\sin{(\theta)}}},\ldots\mspace{14mu},e^{{j{({M - 1})}}\frac{2\pi\; d}{\lambda_{DL}}{\sin{(\theta)}}}} \right\rbrack}^{T}} & (6)\end{matrix}$

In the above equations (5) and (6), λ denotes wavelength, subscripts ULand DL denote uplink and downlink channels respectively, and d denotesantenna spacing. The antenna response vector of the user terminal can beobtained in a similar manner, which will not be described herein.

In a case of a Uniform Planar Array (UPA) of antennas, the antennaresponse vector of base station is:

$\begin{matrix}{{a_{BS}^{UL}\left( {\theta,\phi} \right)} = {\frac{1}{\sqrt{M}}\left\lbrack {1,e^{j\frac{2\pi\; d}{\lambda_{UL}}{({{{\sin{(\theta)}}{\sin{(\phi)}}} + {\cos{(\phi)}}})}},\ldots\mspace{14mu},e^{j\frac{2\pi\; d}{\lambda_{UL}}{({{{({A - 1})}{\sin{(\theta)}}{\sin{(\phi)}}} + {{({B - 1})}{\cos{(\phi)}}}})}}} \right\rbrack}^{T}} & (7) \\{{a_{BS}^{DL}\left( {\theta,\phi} \right)} = {\frac{1}{\sqrt{M}}\left\lbrack {1,e^{j\frac{2\pi\; d}{\lambda_{DL}}{({{{\sin{(\theta)}}{\sin{(\phi)}}} + {\cos{(\phi)}}})}},\ldots\mspace{14mu},e^{j\frac{2\pi\; d}{\lambda_{DL}}{({{{({A - 1})}{\sin{(\theta)}}{\sin{(\phi)}}} + {{({B - 1})}{\cos{(\phi)}}}})}}} \right\rbrack}^{T}} & (8)\end{matrix}$

In the above equations (7) and (8), A denotes the number of antennas inthe horizontal direction, B denotes the number of antennas in thevertical direction, wherein M=A×B is satisfied. The antenna responsevector of the user terminal can be obtained in a similar manner. Since aULA antenna array can also be regarded as a special UPA antenna arraywith B=1, these two types of antenna are not distinguished in thespecification of the present application, and a description will begiven by taking the antenna response vector of a UPA antenna array as anexample.

Based on the reciprocity of antenna arrival angles in uplink anddownlink channels in a FDD system, the present application proposes abeam training method and a device for implementing the method.Information obtained from beam training in the uplink (downlink) channelis used to facilitate the beam training in the downlink (uplink) channelto achieve the purpose of reducing beam training overhead.

FIG. 7a shows a schematic view of an electronic device used for acommunication device in a wireless communication system according to anembodiment of the present disclosure. Here, the communication device maybe a base station or a user equipment. Below, a discussion will be givenwith a communication device being a base station as an example.

As shown in FIG. 7a , the electronic device 700 includes a channelquality estimation unit 701, a sub-codebook generation unit 702, atransmission configuration unit 703, and a storage device 704.

The storage device 704 is used to store an analog codebook of the basestation, which contains a plurality of sets of configuration parameters(i.e., multiple weight vectors) for a set of phase shifters in the basestation.

The channel quality estimation unit 701 can estimate the channel qualityof the uplink channel based on the analog codebook stored in the storagedevice 704 and signal (for example, a pilot signal or a referencesignal, a training signal) from the user equipment. Wherein, thecommunication system to which the present invention is applied is, forexample, an LTE system, and the signal from the user equipment is, forexample, a Sounding Reference Signal (SRS) or an uplink reference signalspecifically and newly defined for analog beamforming.

The sub-codebook generation unit 702 selects, from the analog codebookof the base station, a weight vector which has a corresponding channelquality equal to or higher than a predetermined threshold value based onthe estimation result of the channel quality estimation unit 701,thereby generating an analog sub-codebook. Compared to the analogcodebook of the base station, the analog sub-codebook may only include aportion of the weight vectors in the analog codebook, thereby achievingthe reduction of the analog codebook.

The transmission configuration unit 703 is used for configuring thesignal transmission of the base station, such that the beam training ofdownlink channel between the base station and the user equipment isbased on the analog sub-codebook of base station. That is to say, in thebeam training of the downlink channel, the base station sends a signal(such as pilot signal or reference signal, a training signal) based onthe analog sub-codebook, and the user equipment evaluates the signalquality of the downlink channel according to the signal sent by the basestation, to assist the base station in selecting an optimal weightvector (that is, the configuration parameters of the phase shifters) toperform data transmission of the downlink channel. Wherein, thecommunication system to which the present disclosure is applied is, forexample, an LTE system. A signal sent by the base station is, forexample, a channel state information reference signal (CSI-RS) or adownlink reference signal specifically and newly defined for analogbeamforming, It should be understood that the above is described bytaking the LTE system as an example. However, the technical solution ofthe present application is not limited to LTE system. In differentcommunication systems, the signal sent by the base station may be othersuitable reference signals, as long as beamforming can be performed.

FIG. 7b shows a schematic view of an electronic device used for anothercommunication device in the wireless communication system according toan embodiment of the present disclosure. The another communicationdevice is used for communicating with the communication device of FIG.7a . For example, if the electronic device 700 of FIG. 7a is located ina base station, the another electronic device 710 of FIG. 7b is a userequipment. If the electronic device 700 of FIG. 7a is located in a userequipment, the another electronic device 710 of FIG. 7b is a basestation. Below, a discussion will be given with an example where theelectronic device is located in a user equipment.

As shown in FIG. 7b , the electronic device 710 includes a storagedevice 711, a channel quality estimation unit 712, an analogsub-codebook acquisition unit 713, and a transmission configuration unit714. Wherein, the storage device 711 stores an analog codebook of theuser equipment, which includes a plurality of sets of configurationparameters (i.e., weight vectors) for a set of phase shifters used inthe user equipment.

The transmission configuration unit 714 configures the transmission of asignal (e.g., a pilot signal) from the user equipment to the basestation based on the analog codebook to faciliate the base station tocalculate the channel quality of the uplink channel based on the signal.For example, the transmission configuration unit 714 makes the values ofthe set of phase shifters of the user equipment equal to a set ofconfiguration parameters (i.e., a weight vector) in the analog codebook,and sends a pilot signal to the base station in this case.

The analog sub-codebook acquisition unit 713 is used for acquiring ananalog sub-codebook of the user equipment from the base station. Theanalog sub-codebook is obtained by reducing the analog codebook of theuser equipment. The reducing process of analog codebook will bedescribed in detail later.

The channel quality estimation unit 712 can estimate a channel qualityof the downlink channel according to the analog sub-codebook stored inthe storage device 711 and the signal (for example, a pilot signal) fromthe base station.

Those skilled in the art should understand that the electronic deviceused in the base station and the electronic device used in the userequipment described above may each include a processor or a processingcircuit, by which various functional units are implemented.

FIG. 8 shows a flowchart of performing beam training by using theelectronic device of FIG. 7 in a base station according to an embodimentof the present invention.

As shown in FIG. 8, in step 801, the user equipment reports antennaparameters of the user equipment to the base station. Here, the antennaparameters are, for example, the type of antenna (such as a linearantenna or a planar antenna), antenna spacing and the like. By using theantenna parameters, the base station can calculate the antenna responsevector and the like of the user equipment to calculate a reduced analogcodebook for the user equipment. The user equipment may send the antennaparameters before each beam training or only when accessing the network,In one example, the user equipment reports the antenna parameters of theuser equipment to the base station by using higher layer dedicatedsignaling such as RRC signaling in LIE.

In step 802, the base station broadcasts uplink beam training parametersto the user equipment, for example: start time and end time (e.g.,sub-frame number) of the uplink beam training, the number of times thata training sequence will be transmitted, and the like.

In step 803, the user equipment sends a training sequence to the basestation to perform uplink beam training. In the process of the uplinkbeam training, uplink beam training may be performed by using theexhaustive search method or the single feedback search method describedabove. In addition, in this step, the base station uses the channelquality estimation unit 701 to estimate a channel quality based on thetraining sequence.

FIG. 9 shows a flowchart of performing uplink beam training by using anexhaustive search method according to an embodiment of the presentinvention.

As shown in FIG. 9, in step 901, the user equipment sends an uplink beamtraining sequence based on the uplink beam training parameters from thebase station. Here, the number of times that the training sequence willbe transmitted may depend on the size of the analog codebook of the basestation and the size of the analog codebook of the user equipment. Forexample, if the analog codebook of the base station comprises P weightvectors (that is, the size of the analog codebook of the base station isP), the analog codebook of the user equipment comprises Q weight vectors(that is, the size of the analog codebook of the user equipment is Q),the number of times that the uplink beam training sequence needs to betransmitted is equal to P×Q.

In step 902, the base station estimates an equivalent channel based onthe received training sequence, and calculates an optimal combination ofweight vectors. That is, based on the training sequence, the basestation can calculate which combination may result in the best channelquality among all the combinations between the weight vectors in theanalog codebook of the base station and the weight vectors in the analogcodebook of the user equipment. In subsequent uplink communications, thebase station and the user equipment will communicate by using theselected pair of weight vectors.

In step 903, the base station informs the user equipment of the resultof its calculation. That is, the base station informs the user equipmentwhich weight vector in the analog codebook of the user equipment is tobe used for communications in the uplink channel. In general, the basestation informs the user equipment of the index of the weight vector inthe analog codebook of the user equipment. In another embodiment, thebase station may also inform the user equipment of the index of areceiving weight vector to be used by the base station together.

Through the above steps 901-903, the weight vectors respectively used bythe base station and the user equipment in uplink communication areobtained, so that uplink communication can be performed smoothly.

Besides the exhaustive search method described above, other methods canalso be used. For example, it is possible to use only a part of all thecombinations between the weight vectors in the analog codebook of theuser equipment and the weight vectors in the analog codebook of the basestation. For example, in one embodiment, these combinations maycomprise: combinations between a weight vector in an analog codebook ofthe base station and all weight vectors in the analog codebook of theuser equipment, and combinations between a weight vector in the analogcodebook of the user equipment and all weight vectors in the analogcodebook of the base station. In a preferred embodiment, according tochannel qualities obtained from combinations between one of the weightvectors in the analog codebook of the base station and all the weightvectors in the analog codebook of the user equipment, one weight vectorto be combined with all the weight vectors in the analog codebook of thebase station is selected from the weight vectors in the analog codebookof the user equipment. This is the single feedback search method thatwill be described below.

FIG. 10 shows a flowchart of performing uplink beam training by using asingle feedback search method according to an embodiment of the presentinvention.

As shown in FIG. 10, in step 1001, the user equipment repeatedly sendsan uplink beam training sequence according to the uplink beam trainingparameters sent by the base station. In the single feedback method,since the base station receives the training sequence by using anOmni-directional beam (i.e., using a predetermined weight vector), it isonly necessary to sweep all the weight vectors in the analog codebook ofthe user equipment. Therefore, the uplink beam training sequence will betransmitted for Q times (i.e. equal to the size of the analog codebookof the user equipment), and a different weight vector in the analogcodebook of the user equipment is used each time.

In step 1002, the base station estimates an equivalent channel (e.g., itmay be expressed as f_(omni) ^(T)H^(UL)w) based on the received trainingsequence, where w∈Wc, and calculates a channel quality. The base stationselects a weight vector W_(opt) from the analog codebook of the userequipment that corresponds to the best channel quality as the weightvector to be used by the user equipment in the subsequent uplink channeltransmission.

In step 1003, the base station informs the user equipment of index ofthe weight vector selected in step 1002.

In step 1004, the user equipment continuously sends the uplink beamtraining sequence by using the weight vector selected by the basestation. The base station sweeps all the weight vectors in the analogcodebook of the base station according to the training sequence sent bythe user equipment. Since the base station will sweep all the weightvectors in the analog codebook of the base station based on thesetraining sequences, the training sequence will be repeated P times(i.e., it is equal to the size of the analog codebook of the basestation).

In step 1005, the base station estimates an equivalent channel (e.g., itmay be represented as f^(T)H^(UL)w_(opt)), where f^(T)∈Fc, andcalculates an optimal weight vector f_(opt) in the analog codebook ofthe base station. Here, the base station calculates channel qualitiesobtained with weight vectors in the analog codebook of base stationaccording to the training sequence, and selects a weight vectorcorresponding to an optimal channel quality therefrom as the weightvector for subsequent uplink communication with the user equipment.

In this way, through the above steps 1001-1005, the weight vectors usedby the base station and the user equipment respectively for uplinkcommunication are determined, so that the uplink communication can beperformed by using the determined optimal weight vectors.

Next, return to the flowchart of beam training shown in FIG. 8. In step804, the base station will use the sub-codebook generation unit 702 toreduce the analog codebook to obtain a sub-codebook for reversecommunication.

FIG. 11 shows a flowchart of a method for reducing an analog codebookaccording to an embodiment of the present application.

In step 1101, the base station selects a corresponding channel qualityfor each weight vector in the analog codebook of the base stationaccording to the channel qualities, thereby forming a first set ofchannel qualities. Since the base station has already calculated thechannel qualities in various combinations between the weight vectors inthe analog codebook of the user equipment and the weight vectors in theanalog codebook of the base station based on the received uplink beamtraining sequence, in the case that the number of the weight vectors inthe analog codebook of the user equipment is greater than 1, each weightvector in the analog codebook of the base station will be combined withthe various weight vectors in the analog codebook of the user equipment.As such, each weight vector in analog codebook of the base station maycorrespond to multiple channel qualities. In a preferred embodiment, thehighest one is selected from the channel qualities corresponding to eachweight vector in the analog codebook of the base station. In this way,in the first set of channel qualities, each weight vector in the analogcodebook of the base station has a corresponding channel quality.

In step 1102, the base station selects a corresponding channel qualityfor each weight vector in the analog codebook of the user equipmentaccording to the channel qualities, thereby forming a second set ofchannel qualities. Similarly as above, each weight vector in the analogcodebook of the user equipment may correspond to multiple channelqualities. In a preferred embodiment, the base station selects thehighest one from multiple channel qualities corresponding to each weightvector in the analog codebook of the user equipment. In this way, in thesecond set of channel qualities,, each weight vector in analog codebookof the user equipment has a corresponding channel quality.

In step 1103, first predetermined number of channel qualities areselected from the first set of channel qualities and an analogsub-codebook of the base station is generated according to the weightvectors corresponding to the first predetermined number of channelqualities. Here, the specific numerical value of the first predeterminednumber may be selected according to the size of the analog codebook ofthe base station. For example, if the analog codebook of the basestation contains a very large number (for example, 2000) of weightvectors, in order to reduce the beam training overhead, only a smallportion of them may be selected (it can be determined according torequirements on system performance, for example, 20). In anotherexample, it is also possible to additionally take the size of the analogcodebook of the user equipment into consideration. The overhead of beamtraining is also related to the size of the analog codebook of the userequipment. Therefore, when determining the specific numerical value ofthe first predetermined number, the size of the analog codebook of thebase station and the size of the analog codebook of the user equipmentmay be considered at the same time.

In step 1104, a second predetermined number of channel qualities areselected from the second set of channel qualities, and an analogsub-codebook of user terminal is generated according to the weightvectors corresponding to the second predetermined number of channelqualities. Similar to step 1103, the specific numerical value of thesecond predetermined number may be selected according to the size of theanalog codebook of the user equipment. In another example, it is alsopossible to additionally take the size of the analog codebook of thebase station into consideration.

In the method described above with reference to FIG. 11, it is notnecessary to perform the various steps sequentially, and some steps maybe performed in parallel. For example, steps 1101 and 1102 may beperformed simultaneously, and steps 1103 and 1104 may also be performedsimultaneously.

Next, return to FIG. 8. Subsequently, in step 805, the base stationinforms the user equipment of the analog sub-codebook of the userequipment generated in step 1104. In one example, the base station doesnot have to send the analog sub-codebook of the user equipment itself,instead it only needs to send indexes of the analog sub-codebook toreduce signaling overhead. Based on the indexes, the user equipment candetermine which weight vectors are included in the analog sub-codebook.

In step 806, the base station sends the parameters of the downlink beamtraining to the user equipment. As described above, in the FDD system,since the uplink and downlink channels do not have reciprocity, it isnecessary to perform uplink and downlink beam training separately.Therefore, before continue to performing downlink beam training, thebase station needs to send the parameters of the downlink beam trainingto the user equipment. Here, the parameters of downlink beam trainingcomprise, for example, start time and end time of downlink beamtraining, the number of times that a training sequence will betransmitted, and the like.

In step 807, downlink beam training is performed between the basestation and the user equipment. In the training process, the basestation uses the analog sub-codebook determined in step 1103 of FIG. 11,and the user equipment uses the analog sub-codebook determined in step1104 of FIG. 11. Since both the base station and the user equipment usethe analog sub-codebooks for downlink beam training, the overhead ofdownlink beam training is reduced.

The process of downlink beam training is similar to the uplink beamtraining except using different analog codebooks. For example, theexhaustive search and single feedback search methods can also be used indownlink beam training.

FIG. 12 shows a flowchart of performing downlink beam training by usingthe exhaustive search method. As shown in FIG. 12, in step 1201, thebase station repeatedly sends a training sequence for downlinkbeamforming. Here, the number of times that the training sequence willbe transmitted may depend on the size of the analog sub-codebook of thebase station and the size of the analog sub-codebook of the userequipment. For example, if the analog sub-codebook of the base stationcomprises Ps weight vectors, and the analog sub-codebook of the userequipment comprises Qs weight vectors, the number of times that thetraining sequence for downlink beamforming needs to be transmitted isequal to Ps×Qs,

In step 1202, the user equipment estimates an equivalent channel basedon the received training sequence and calculates an optimal combinationof weight vectors. That is, based on the training sequence, the userequipment can calculate which combination may result in the best channelquality among all the combinations between the various weight vectors inthe analog sub-codebook of the base station and the various weightvectors in the analog sub-codebook of the user equipment. In subsequentdownlink communications, the base station and the user equipment willcommunicate by using the selected pair of weight vectors.

In step 1203, the user equipment informs the base station of the resultof its calculation. That is, the user equipment informs the base stationwhich weight vector in the analog sub-codebook of the base station is tobe used for the communications in the downlink channel. In general, theuser equipment informs the base station of an index of the weight vectorin the analog sub-codebook of the base station. In another embodiment,the user equipment may also inform the base station of an index of theweight vector to be used by the user equipment together.

Through the above steps 1201-1203, the weight vectors used by the basestation and the user equipment respectively in downlink communicationare obtained, so that downlink communication can be performed smoothly.

FIG. 13 shows a flowchart of performing downlink beam training using thesingle feedback search method.

As shown in FIG. 13, in step 1301, the base station repeatedly sends adownlink beam training sequence according to downlink beam trainingparameters. In the single feedback method, since the user equipmentreceives the training sequence by using an Omni-directional beam (i.e.,using a predetermined weight vector), it is only necessary to sweep allthe weight vectors in the analog sub-codebook of the base station.Therefore, the downlink beam training, sequence will be transmitted forPs times (i.e. it is equal to the size of the analog sub-codebook of thebase station), by using a different weight vector in the analogsub-codebook of the base station each time.

In step 1302, the user equipment estimates an equivalent channel basedon the received training sequence and calculates a channel quality. Theuser equipment selects a weight vector from the analog sub-codebook ofthe base station that corresponds to the best channel quality as theweight vector to be used by the base station in the subsequent downlinkchannel transmission.

In step 1303, the user equipment informs the base station of an index ofthe weight vector selected in step 1302.

In step 1304, the base station sends the downlink beam training sequenceby using the weight vector selected by the base station. The userequipment sweeps all the weight vectors in the analog sub-codebook ofthe user equipment according to the training sequence sent by the basestation. Since the user equipment will sweep all the weight vectors inthe analog sub-codebook of the user equipment based on these trainingsequences, the training sequences will be repeated Qs times (i.e., it isequal to the size of the analog sub-codebook of the user equipment).

In step 1305, the user equipment estimates an equivalent channel andcalculates an optimal weight vector in the analog sub-codebook of theuser equipment. Here, the user equipment calculates channel qualitiesobtained with various weight vectors in the analog sub-codebook of theuser equipment according to the training sequence, and selects a weightvector corresponding to an optimal channel quality therefrom as theweight vector for subsequent downlink communication with the basestation.

In this way, through the above steps 1301-1305, the weight vectors usedby the base station and the user equipment respectively for downlinkcommunication are determined, so that downlink communication can beperformed by using the determined optimal weight vectors.

FIG. 14 shows an example of reducing an analog codebook with anexhaustive search algorithm.

As shown in FIG. 14, by using an exhaustive search algorithm in theuplink beam training, the base station can obtain channel qualitiesc_(i,j)=|f^(i,T)H^(UL)w^(j)| under all combinations of the weightvectors, wherein 1≤i≤P, 1≤j≤Q. Wherein a_(i) is the best channel qualityreached by the base station when its weight vector is f, i.e.,

${a_{i} = {\max\limits_{j}c_{i,j}}},{1 \leq i \leq {P.}}$

b_(j) is the best channel quality reached by the user equipment when itsweight vector is w^(j), i.e.,

${b_{j} = {\max\limits_{i}c_{i,j}}},{1 \leq j \leq {Q.}}$

After obtaining the sets {a₁,a₂, . . . ,a_(P)}and {b₁,b₂, . . . ,b_(Q)},the largest Ps elements and Qs elements are selected therefromrespectively, and the corresponding weight vectors form the analogsub-codebook of the base station and the analog sub-codebook of the userequipment. In the example of FIG. 14, P=Q=4, Ps=Qs=2, and the graypositions in the figure indicate the indexes of the weight vectors inthe obtained analog sub-codebooks.

FIG. 15 shows an example of reducing an analog codebook with a singlefeedback search algorithm.

As shown in FIG. 15, in the single feedback search algorithm, the userequipment sweeps all the weight vectors w^(j),1≤j≤Q in the analogcodebook of the user equipment, and the base station receives andmeasures channel qualities by using an omni-directional beam f_(omni),and selects therefrom a weight vector resulting in the best channelquality (w_(opt)=argmax|f_(omni) ^(T)H^(UL)w|, wherein w∈Wc) and feedsit back to the user equipment. Then, the user equipment uses the optimalweight vector w_(opt) fixedly, and the base station sweeps all theweight vectors f^(i), 1≤i≤P in the analog codebook of the base station,and selects a weight vector resulting in the best channel qualitytherefrom (f_(opt)=argmax|f^(T)H^(UL)w_(opt)|, wherein f ∈ Fc).Therefore, if the single feedback algorithm is used in uplink beamtraining, the base station can only obtain channel quality informationunder a part of the combinations between the weight vectors of the basestation and the user equipment, in this case,a_(i)=|f^(i,T)H^(UL)w_(opt)|, b_(j)=|f_(omni) ^(T)H^(UL)w^(j)|. Thelargest Ps elements and Qs elements are respectively selected from sets{a₁,a₂, . . . a_(P)} and {b₁,b₂, . . . ,b_(Q)}, and weight vectorscorresponding thereto form the analog sub-codebook Fs of the basestation and the analog sub-codebook Ws of the user equipment. As shownin FIG. 15. P=Q=4, Ps=Qs=2, and the gray positions in the figureindicate the indexes of the weight vectors in the obtained analogsub-codebooks.

All the above description is to reduce the analog codebook(s) of thebase station and/or the user equipment based on uplink beam training, soas to obtain the analog sub-codebooks used for downlink communication ofthe base station and/or the user equipment. The overhead of downlinkbeam training is reduced by using analog sub-codebooks in downlink beamtraining. However, the particular implementations of the presentapplication are not limited to the above embodiments. Those skilled inthe art should understand that the analog codebook(s) of the basestation and/or the user equipment may also be reduced based on downlinkbeam training to obtain the analog sub-codebook(s) of the base stationand/or the user equipment. The overhead of uplink beam training isreduced by using analog sub-codebooks in the process of uplink beamtraining.

In addition, in the above embodiment, both the analog codebook of thebase station and the analog codebook of the user equipment are reduced.In practical applications, the technical effect of reducing the beamtraining overhead can also be achieved by only reducing the analogcodebook of the base station or only reducing the analog codebook of theuser equipment.

Further, in another embodiment of the present application, the analogsub-codebooks of the base station and the user equipment may further becorrected.

FIGS. 16a and 16b are schematic views respectively showing theelectronic device structures used for a base station and a userequipment according to another embodiment of the present application.

As shown in FIG. 16a , the electronic device used for the base stationcomprises a channel quality estimation unit 1601, a sub-codebookgeneration unit 1602, a correction unit 1605, a transmissionconfiguration unit 1603, and a storage device 1604. Wherein, the channelquality estimation unit 1601, the sub-codebook generation unit 1602 thetransmission configuration unit 1603, and the storage device 1604 aresimilar to the channel quality estimation unit 701, the sub-codebookgeneration unit 702, the transmission configuration unit 703, and thestorage device 704 shown in FIG. 7a , and the same functions of thesecomponents will not be repeated herein.

The correction unit 1605 may comprise a first correction unit (notshown). Wherein, the first correction unit is used to correct the analogsub-codebook of the base station. In addition, in another embodiment,the correction unit 1605 may further comprise a second correction unit(not shown) for correcting the analog sub-codebook of the userequipment.

The correction processes of the first correction unit and the secondcorrection unit will be separately described below, still with anexample in which analog codebook used in downlink beam training isreduced by uplink beam training.

In the correction process of the first correction unit, the analogsub-codebook of the base station will be corrected according to anuplink signal transmission frequency between the base station and theuser equipment, and the corrected analog sub-codebook is used to performthe downlink beam training.

The specific steps are as shown in FIG. 17 In step 1701 for each weightvector in the analog sub-codebook of the base station, a horizontalarrival angle and a vertical arrival angle that minimizes the distancebetween the weight vector and each base station terminal antennaresponse vector of the uplink channel is calculated. That is, for aweight vector f_(in) in the analog sub-codebook of the base station, itscorresponding horizontal arrival angle θ_(in) and vertical arrival angleφ_(in) are calculated, which satisfy the following conditions

$\left\{ {\theta_{in},\varphi_{in}} \right\} = {\underset{\theta,\varphi}{argmin}{{f_{in} - {a_{BS}^{UL}\left( {\theta,\varphi} \right)}}}_{2}}$

Wherein a_(BS) ^(UL)(θ,φ) is the base station terminal antenna responsevector of the uplink channel.

In step 1702, by using the reciprocity between the antenna arrivalangles of the uplink and downlink channels in the FDD system, a firstantenna response vector of the base station terminal of the downlinkchannel corresponding to the horizontal arrival angle θ_(in) and thevertical arrival angle φ_(in) calculated in step 1701 is obtained.

In step 1703, a weight vector having the smallest distance from thefirst antenna response vector described above is selected from theanalog codebook of the base station as a corrected weight vector. Thatis to say, suppose the corrected weight vector is f_(out), then

$f_{out} = {\underset{f \in F}{argmin}{{f - {a_{BS}^{DL}\left( {\theta_{in},\varphi_{in}} \right)}}}_{2}}$

Wherein a_(BS) ^(DL)(θ,φ) is the base station terminal antenna responsevector of the downlink channel, and F is the analog codebook of the basestation.

The above correction process is performed for each weight vector in theanalog sub-codebook of base station to finally obtain a corrected analogsub-codebook. The transmission configuration unit 703 will use thecorrected analog sub-codebook to configure the base station so that thebase station uses the corrected analog sub-codebook in downlink beamtraining.

In the correction process of the second correction unit, the analogsub-codebook of the user equipment will be corrected according to anuplink signal transmission frequency between the base station and theuser equipment and the antenna configuration of the user equipment, andthe corrected analog sub-codebook is used to perform downlink beamtraining. Correspondingly, the base station will inform the userequipment of the corrected analog sub-codebook of the user equipment(for example through step 805 shown in FIG. 8). As a variation of theexample, the second correction unit is provided on the user equipmentside instead of the base station side, that is, after the user equipmentobtains an uncorrected analog sub-codebook, it can correct the analogsub-codebook according to the uplink signal transmission frequency byitself. In this example, the user equipment does not need to inform thebase station of its antenna configuration information, thereby reducingsignaling overhead. When the second correction unit is provided on theuser equipment side, the base station will inform the user equipment ofa pre-corrected analog sub-codebook of user equipment (for example,through step 805 of FIG. 8).

The specific steps are as shown in FIG. 18. In step 1801, for eachweight vector in the analog sub-codebook of the user equipment, ahorizontal arrival angle and a vertical arrival angle that minimizes thedistance between the weight vector and each user equipment terminalantenna response vector of the uplink channel is calculated. For aweight vector w_(in) in the analog sub-codebook of the user equipment,its corresponding horizontal arrival angle θ_(in) and a vertical arrivalangle φ_(in) are calculated, which satisfy the following condition:

$\left\{ {\theta_{in},\varphi_{in}} \right\} = {\underset{\theta,\varphi}{argmin}{{w_{in} - {a_{UE}^{UL}\left( {\theta,\varphi} \right)}}}_{2}}$

Wherein a_(UE) ^(UL)(θ,φ) is the user equipment terminal antennaresponse vector of the uplink channel.

In step 1802, by using the reciprocity between the antenna arrivalangles of the uplink and downlink channels in the FDD system, a secondantenna response vector of the user equipment terminal of the downlinkchannel corresponding to the horizontal arrival angle and the verticalarrival angle calculated in step 1801 is obtained.

In step 1803, a weight vector having the smallest distance from thesecond antenna response vector is selected from the analog codebook ofthe user equipment as a corrected weight vector. That is to say, supposethe corrected weight vector is w_(out), then it satisfies

$w_{out} = {\underset{w \in W}{argmin}{{w - {a_{UE}^{DL}\left( {\theta_{in},\varphi_{in}} \right)}}}_{2}}$

Where a_(UE) ^(DL)(θ,φ) is the user equipment terminal antenna responsevector of the downlink channel, and W is the analog codebook of the userequipment.

As described above, the analog sub-codebooks of the base station and theuser equipment are corrected according to the uplink signal transmissionfrequency between the base station and the user equipment and theantenna configuration of the user equipment, and downlink beam trainingis performed by using the corrected analog sub-codebook.

In another embodiment, firstly, downlink beam training is performed, andthe analog codebook(s) of the base station and/or the user equipment isreduced based on the result of the downlink beam training to obtain ananalog sub-code book(s) for uplink communication of the base stationand/or the user equipment. In such an embodiment, as shown in FIG. 16b ,a correction unit 1615 may also be disposed in the electronic device ofthe user equipment, the analog sub-codebook of the user equipment iscorrected according to an uplink signal transmission frequency betweenthe base station and the user equipment and the antenna configuration ofthe user equipment, and uplink beam training is performed by using thecorrected analog sub-codebook. Optionally, the correction unit 1615 mayalso correct the analog sub-codebook of the base station according tothe uplink signal transmission frequency between the base station andthe user equipment and the antenna configuration of the base station, sothat the base station performs uplink beam training by using thecorrected analog sub-codebook. It can be understood that the userequipment may inform the base station of an uncorrected analogsub-codebook of base station, and the base station may correct it byitself.

The specific steps of correcting the analog sub-codebook of the basestation used for uplink beam training based on the result of downlinkbeam training are shown in FIG. 19. In step 1901, for each weight vectorin the analog sub-codebook of the base station, a horizontal arrivalangle and a vertical arrival angle that minimizes the distance betweenthe weight vector and each base station terminal antenna response vectorof the downlink channel are calculated. That is, for a weight vectorf_(in) in the analog sub-codebook of the base station, its correspondinghorizontal arrival angle θ_(in) and a vertical arrival angle φ_(in) arecalculated, which satisfy the following conditions

$\left\{ {\theta_{in},\varphi_{in}} \right\} = {\underset{\theta,\varphi}{argmin}{{f_{in} - {a_{BS}^{DL}\left( {\theta,\varphi} \right)}}}_{2}}$

Where a_(BS) ^(DL)(θ,φ) is the base station terminal antenna responsevector of the downlink channel.

In step 1902, according to the reciprocity between the antenna arrivalangles of the uplink and downlink channels in the FDD system, a thirdantenna response vector of the base station terminal of θ_(in) and thevertical arrival angle φ_(in) calculated in step 1901 is obtained.

In step 1903, a weight vector having the smallest distance from thethird antenna response vector is selected from the analog codebook ofthe base station as a corrected weight vector. That is to say, supposethe corrected weight vector is f_(out), then

$f_{out} = {\underset{f \in F}{argmin}{{f - {a_{BS}^{UL}\left( {\theta_{in},\varphi_{in}} \right)}}}_{2}}$

Where a_(BS) ^(UL)(θ,φ) is the base station terminal antenna responsevector of the uplink channel, and F is the analog codebook of the basestation.

The above correction process is performed for each weight vector in theanalog sub-codebook of the base station to finally obtain a correctedanalog sub-codebook. The transmission configuration unit 703 will usethe corrected analog sub-codebook to configure the base station, so thatthe base station uses the corrected analog sub-codebook in uplink beamtraining.

The steps of correcting the analog sub-codebook of the user equipmentfor uplink beam training based on a result of downlink beam training isshown in FIG. 20. As shown in FIG. 20, in step 2001, for each weightvector in the analog sub-codebook of the user equipment, a horizontalarrival angle and a vertical arrival angle that minimizes the distancebetween the weight vector and each user equipment terminal antennaresponse vector of the downlink channel are calculated. For a weightvector w_(in) in the analog sub-codebook of the user equipment, itscorresponding horizontal arrival angle θ_(in) and vertical arrival angleφ_(in) are calculated, which satisfy:

$\left\{ {\theta_{in},\varphi_{in}} \right\} = {\underset{\theta,\varphi}{argmin}{{w_{in} - {a_{UE}^{DL}\left( {\theta,\varphi} \right)}}}_{2}}$

Wherein a_(UE) ^(DL)(θ,φ) is the user equipment terminal antennaresponse vector of the downlink channel.

In step 2002, by using the reciprocity between the antenna arrivalangles of the uplink and downlink channels in the FDD system, a fourthantenna response vector of the user equipment terminal of the uplinkchannel corresponding to the horizontal arrival angle and the verticalarrival angle calculated in step 2001 is obtained.

In step 2003, a weight vector having the smallest distance from thefourth antenna response vector is selected from the analog codebook ofthe user equipment as a corrected weight vector. That is to say, supposethe corrected weight vector is w_(out), then it satisfies:

$w_{out} = {\underset{w \in W}{argmin}{{w - {a_{UE}^{UL}\left( {\theta_{in},\varphi_{in}} \right)}}}_{2}}$

Wherein a_(UE) ^(UL)(θ,φ) is the user equipment terminal antennaresponse vector of the uplink channel, and W is the analog codebook ofthe user equipment.

In one embodiment according to the present application, the horizontalarrival angle θ and the vertical arrival angle φ may be discretized,e.g., they are limited to:

$\theta \in \left\{ {0,{\frac{1}{K_{W}}\pi},\ldots\mspace{14mu},{\frac{\left( {K_{W} - 1} \right)}{K_{W}}\pi}} \right\}$$\varphi \in \left\{ {{{- \frac{1}{2}}\pi},{{{- \frac{1}{2}}\pi} + {\frac{1}{K_{H}}\pi}},\ldots\mspace{14mu},{{{- \frac{1}{2}}\pi} + {\frac{\left( {K_{H} - 1} \right)}{K_{H}}\pi}}} \right\}$

That is, the horizontal arrival angle and the vertical arrival angle aresampled, with K_(W) and K_(H) representing the numbers of the samplingpoints respectively. In one embodiment, K_(W)=2W and K_(H)=2H, wherein Wis the number of antennas in the horizontal direction and H is number ofantennas in the vertical direction.

When the analog sub-codebooks of the base station and the user equipmentare obtained through uplink beam training and are prepared to be used indownlink beam training, the weight vectors of the base station and theuser equipment should be selected from the corresponding analogsub-codebooks. Downlink beam training may use any training algorithm,but it is constrained to be performed in the analog sub-codebook. Forexample, if the exhaustive search algorithm is used in downlink beamtraining, Ps×Qs weight vector pairs need to be detected, and thecomplexity is reduced from P×Q to Ps×Qs. If the single feedbackalgorithm is used in downlink beam training, the complexity is reducedfrom P+Q to Ps+Qs.

In addition, taking the amount of data and user-specific requirementsinto consideration, the notifications about the analog sub-codebookswhich are referred to in the present invention may be carried by thefollowing signaling in, for example, an LTE system: for example, thededicated signaling carried by the downlink shared channel DL-SCH or theuplink shared channel UL-SCH of the MAC layer or the RRC (Radio ResourceControl) layer and the like, wherein the MAC layer signaling is moretime efficient than the RRC layer signaling, and has a faster decodingrate; the RRC layer signaling is easier to implement than the MAC layersignaling. Specifically, in an example of using the MAC layer dedicatedsignaling to carry notifications about an analog sub-codebook, it isspecifically indicated by bits included in a specific MAC controlelement in one or more MAC protocol data units (PDUs) (for example,which are coded to indicate the index of each weight vector), and aspecial LCID can be set for the MAC control element to identify itsnotifications for an analog sub-codebook. In an example of using RRClayer dedicated signaling to carry notifications about an analogsub-codebook, indexes of weight vectors included in the analogsub-codebook are indicated by information in a radio resource controlinformation unit specifically, for example. The notification about ananalog sub-codebook involves step 805 in FIG. 8, step 903 in FIG. 9,step 1003 in FIG. 10, step 1203 in FIG. 12, and step 1303 in FIG. 13,for example.

To further illustrate the present invention, a more specific embodimentis given below.

Consider a single-cell multi-user millimeter-wave large-scale antennasystem working in FDD mode, a base station uses a hybrid precodingarchitecture and serves K users at the same time, with K RF linksprovided on the base station terminal and zero-forcing (ZF) precodingused in its digital portion. Both of the base station and the userequipment terminals are equipped with a ULA antenna array, with numbersof antennas of M and N respectively, and both of them use the designscheme of the classical DFT beamforming codebook. The codebook isdetermined by the following codebook matrix

${\lbrack C\rbrack_{i,m} = j^{\lfloor\frac{i \times {({{({m + {N_{c}/2}})}{modN}_{c}}}}{N_{c}/4}\rfloor}},{1 \leq i \leq N_{a}},{1 \leq m \leq N_{c}}$

Here, N_(a) represents the number of antennas and N_(c) represents thesize of the codebook. Specific system simulation parameters are shown inthe following table:

TABLE 1 specific simulation parameters the number M of antennas of basestation 64 the number N of antennas of user equipment terminal 8 thenumber K of users in the cell 4 the size P of codebook for beamformingin base station 128 terminal the size Q of codebook for beamforming inuser 16 equipment terminal channel parameters {N_(cl), N_(ray)} {1, 3},{3, 8} standard deviation of channel angle spread 8° uplink channelwavelength λ_(UL) 2d downlink channel wavelength λ_(DL)$\frac{10}{9}\lambda_{UL}$

Suppose the OFDM parameters specified in LTE are used for transmission,with one time slot being 0.5 ms which includes 7 OFDM symbols. Due tothe restriction of physical conditions, a phase shifter cannot beswitched within one OFDM symbol period, thus each OFDM symbol can beused to detect one combination of weight vectors. In addition, it isassumed that the period of beam searching is 0.5 s. It can be calculatedthat each period of beam searching contains B=7000 OFDM symbols.

Considering the traditional exhaustive search mechanism, the overhead oficy beam training is PQ OFDM symbols. However, the reduced codebookbased beam training mechanism proposed herein can reduce the trainingoverhead to PsQs OFDM symbols.

In order to verify the performance of the reduced codebook basedtraining mechanism proposed herein, a simulation of the averageachievable rate of users is given below, wherein a total of four schemesare considered: (1) Ps=12, Qs=2, with weight vector correction: (2)Ps=12, Qs=2, without weight vector correction; (3) Ps=8, Qs=1, withweight vector correction; (4) Ps=8, Qs=1, without weight vectorcorrection.

The following table shows a training overhead comparison between theconventional scheme and the scheme proposed in the present invention,expressed as a percentage:

scheme training overhead traditional scheme 29.26% reduced codebookscheme, P_(s) = 12, Q_(s) = 2 0.34% reduced codebook scheme, P_(s) = 8,Q_(s) = 1 0.11%

As can be seen from the above table, the beam training method of thepresent application can greatly reduce the overhead of downlink (uplink)beam training.

In consideration of the training overhead, FIG. 21 shows the averageachievable rate of users of several schemes when the channel conditionsare N_(cl)=1 and N_(ray)=3. It can be seen that since the analogsub-codebook based beam training scheme can greatly reduce the beamtraining overhead, the average achievable rate of users is increasedcompared to the conventional scheme, showing that the beam trainingmethod proposed in this application can improve the performance of theFDD system. In addition, it can be noted that, under the condition ofthe same analog sub-codebook size, the scheme with correction has asignificant performance gain compared to the scheme without correction,and therefore a correction step is included in the preferred embodimentof generating an analog sub-codebook.

FIG. 22 shows the average achievable rate of users of several schemeswhen the channel conditions are N_(cl)=3 and N_(ray)=8, from which asimilar conclusion can be obtained. Meanwhile, it should also be noticedthat, compared to the situation with channel conditions ofN_(cl)=1,N_(ray)=3, the performance gain is slightly degraded,especially when Ps=8 and Qs=1, thus when there are many channelscatterers, the size of the analog sub-codebook may be appropriatelyincreased to guarantee the performance. In other words, the size of theanalog sub-codebook may optionally be changed dynamically, for example,dynamically adjusted according to a current application scenario or achange in the performance of a monitored system. The adjustment may beperformed by a network-side device, for example set by a base stationaccording to a program, or configured by an operator, and notified to apeer communication device such as a user equipment through broadcast ordedicated control signaling, so that the peer communication device mayselect a corresponding number of configuration parameters as an analogsub-codebook.

Application Example

The technology of the present disclosure can be applied to variousproducts. For example, the base station may be implemented as any typeof evolved Node B (eNB), such as a macro eNB and a small eNB. A smalleNB may be an eNB that covers cells smaller than the macro cells, suchas a pico eNB, a micro eNB, or a home (femto) eNB. Instead, the basestation may be implemented as any other type of base station, such as aNodeB and a Base Transceiver Station (BTS). The base station maycomprise: a main body configured to control wireless communication (alsoreferred to as a base station device, such as the electronic devices 700and 710 described in this application); and one or more remote radioheads (RRHs) that are located in different locations from the main body.In addition, various types of terminals described below may operate as abase station by temporarily or semi-permanently performing the functionsof a base station.

For example, the terminal device may be implemented as a mobile terminalsuch as a smart phone, a tablet personal computer (PC), a notebook PC, aportable game terminal, a portable/dongle type mobile router and adigital camera; or an on-board terminal such as a car navigation device.The terminal device may also be implemented as a terminal performingmachine-to-machine (M2M) communication (also referred to as a machinetype communication (MTC) terminal). In addition, the terminal device maybe a wireless communication module (such as an integrated circuit moduleincluding a single wafer, for example, the electronic devices 700 and710 described in the present application) installed on each of theaforementioned terminals.

FIG. 23 shows an example of a hardware configuration of the electronicdevice according to the present invention.

The central processing unit (CPU) 2301 functions as a data processingunit that executes various types of processing based on programs storedon read only memory (ROM) 2302 or a storage unit 2308. For example, theCPU 2301 executes processing based on the aforementioned sequence. Therandom access memory (RAM) 2303 stores programs, data and the likeexecuted by the CPU 2301. The CPU 2301, the ROM 2302, and the RAM 2303are connected to one another via a bus 2304.

The CPU 2301 is connected to the input and output interface 2305 via bus2304, and an input unit 2306 composed of various types of switches, akeyboard, a mouse, a microphone and the like and an output unit 2307composed of a display, a speaker and the like are connected to the inputand output interface 2305. For example, the CPU 2301 executes varioustypes of processing in response to instructions inputted from the inputunit 2306, and outputs the processing results to the output unit 2307.

The storage unit 2308 connected to the input and output interface 2305is constituted by a hard disk, for example, and stores programs executedby the CPU 2301 and various kinds of data thereon. The communicationunit 2309 communicates with external devices via a network such as theInternet or a local area network.

The driver 2310 connected to the input and output interface 2305 drivesa removable medium 2311 such as a magnetic disk, an optical disk, amagneto-optical disk, or semiconductor memory (for example, a memorycard) and the like, and acquires various types of data such as contentand key information recorded thereon. For example, by using the acquiredcontent and key data, processings such as beam training for wirelesscommunication and the like are performed by the CPU 2301 based on areproduction program.

The method and system of the present invention may be implemented inmany ways. For example, the method and system of the present inventionmay be implemented by software, hardware, firmware, or any combinationof software, hardware and firmware. The above sequence of steps of themethod is merely for the purpose of illustration, and the steps of themethod of the present invention are not limited to the above-describedspecific order unless otherwise specified. In addition, in someembodiments, the present invention may also be implemented as programsrecorded in a recording medium, wherein these programs includemachine-readable instructions for implementing the method according tothe present invention. Thus, the present invention also covers arecording medium storing programs for executing the method according tothe present invention.

Finally, the present application may be implemented in the followingways.

(1) An electronic device for a first communication device in a wirelesscommunication system, the electronic device comprising:

storage device configured to store an analog codebook for the firstcommunication device, the analog codebook comprising a plurality of setsof configuration parameters for a set of phase shifters of the firstcommunication device: and

a processing circuit configured to:

-   -   performing channel estimation on a first channel from a second        communication device to the first communication device        respectively based on the plurality of sets of configuration        parameters and pilot signal transmission from the second        communication device,    -   selecting a set of configuration parameters corresponding to        ones of the channel estimation results that satisfy a        predetermined condition to generate a reduced analog        sub-codebook,    -   configuring a pilot signal transmission from the first        communication device to the second communication device based on        the analog sub-codebook, to be used in channel estimation on a        second channel from the first communication device to the second        communication device.

(2). The electronic device according to (1), wherein each set of theplurality of sets of configuration parameters corresponds to a weightvector, and each weight vector is used to configure a phase value foreach phase shifter in the set of phase shifters.

(3). The electronic device according to (1), wherein the processingcircuit is further configured to correct the reduced analog sub-codebookbased on a signal transmission frequency between the first communicationdevice and the second communication device to obtain a corrected analogsub-codebook, and configure the pilot signal transmission from the firstcommunication device to the second communication device by using thecorrected analog sub-codebook.

(4). The electronic device according to (1), wherein the storage deviceis further configured to store a peer analog codebook for the secondcommunication device, the peer analog codebook comprising a plurality ofsets of configuration parameters for a set of phase shifters of thesecond communication device:

the processing circuit is further configured to (a peer sub-codebookgeneration unit) select a set of configuration parameters of the secondcommunication device corresponding to ones of the channel estimationresults that satisfy a predetermined condition to generate a reducedpeer analog sub-codebook for the second communication device, whereinthe second communication device configures reception of pilot signalfrom the first communication device to the second communication devicebased on the peer analog sub-codebook.

(5). The electronic device according to (4), wherein the processingcircuit is further configured to correct the reduced peer analogsub-codebook based on a signal transmission frequency between the firstcommunication device and the second communication device and an antennaconfiguration of the second communication device to obtain a correctedpeer analog sub-codebook, wherein the corrected peer analog sub-codebookis used by the second communication device to configure reception ofpilot signal from the first communication device to the secondcommunication device.

(6). The electronic device according to (4), wherein the processingcircuit is further configured to, before configuring the pilot signaltransmission from the first communication device to the secondcommunication device, generate a message about the peer analogsub-codebook to inform the second communication device.

(7). The electronic device according to any one of (1) to (6), whereinthe processing circuit is further configured to determine one set of theplurality of sets of configuration parameters for configuring datasignal transmission through the second channel based on feedback ofchannel estimation of the second channel provided by the secondcommunication device, wherein the feedback of channel estimationincludes a channel estimation result corresponding to a set ofconfiguration parameters having an optimal channel performance.

(8). The electronic device according to (7), wherein the electronicdevice operates as the first communication device, and further comprisesthe set of phase shifters, a radio frequency link, and a plurality ofantennas, wherein the set of phase shifters are disposed between theradio frequency link and the plurality of antennas, wherein theprocessing circuit configures phases of the set of the phase shiftersbased on the analog sub-codebook, and uses the plurality of antennas totransmit pilot signal to the second communication device.

(9). The electronic device according to (8), wherein the firstcommunication device is a base station, the second communication deviceis a user equipment, the first channel corresponds to an uplink channel.and the second channel corresponds to a downlink channel.

(10). The electronic device according to (8), wherein the firstcommunication device is a user equipment, the second communicationdevice is a base station, the first channel corresponds to a downlinkchannel, and the second channel corresponds to an uplink channel.

(11). The electronic device according to (9), wherein the processingcircuit is further configured to, before performing the channelestimation of the first channel from the second communication device tothe first communication device, generate a control message forconfiguring pilot signal transmission of the second communicationdevice, the control message including control parameters of the pilotsignal transmission.

(12) The electronic device according to (9), wherein the electronicdevice comprises a plurality of radio frequency links, each of the radiofrequency links is coupled to a set of phase shifters, and theelectronic device further comprises a digital precoder coupled to theplurality of radio frequency links; the processing circuit is furtherconfigured to generate a digital precoding matrix based on feedback ofchannel estimation from a plurality of the second communication devices,to enable the digital precoder to perform digital precoding of datasignals for the plurality of second communication devices.

(13) The electronic device according to (1), wherein the wirelesscommunication system is a frequency division duplex communicationsystem.

(14) An electronic device for a second communication device in awireless communication system, comprising:

storage device configured to store an analog codebook for the secondcommunication device, the analog codebook comprising a plurality of setsof configuration parameters for a set of phase shifters of the secondcommunication device; and a processing circuit configured to:

-   -   configuring pilot signal transmission from the second        communication device to a first communication device based on        the plurality of sets of configuration parameters, to be used in        channel estimation of a first channel from the second        communication device to the first communication device,    -   obtaining, from the first communication device, a reduced analog        sub-codebook for the second communication device, the analog        sub-codebook being generated by the first communication device        based on a set of configuration parameters corresponding to ones        of channel estimation results on the first channel that satisfy        a predetermined condition,    -   configuring reception of pilot signal from the first        communication device based on the analog sub-codebook, and        performing channel estimation of a second channel from the first        communication device to the second communication device.

(15). A beam training method for frequency division duplex FDDmillimeter wave communication, comprising:

sending, by a user equipment, an uplink training sequence to a basestation according to a user terminal codebook;

receiving, by the base station, the uplink training sequence andcalculating channel qualities under multiple combinations between weightvectors in the user terminal codebook and weight vectors in a basestation terminal codebook;

selecting a corresponding channel quality for each weight vector in thebase station terminal codebook according to the channel qualities toform a first channel quality set;

selecting a corresponding channel quality for each weight vector in theuser terminal codebook according to the channel qualities to form asecond channel quality set;

selecting a first predetermined number of channel qualities from thefirst channel quality set and generating a reduced base station terminalcodebook based on the weight vectors corresponding to the firstpredetermined number of channel qualities;

selecting a second predetermined number of channel qualities from thesecond channel quality set and generating a reduced user equipmentterminal codebook based on the weight vectors corresponding to thesecond predetermined number of channel qualities; and

performing downlink beam training using the reduced base stationterminal codebook and the reduced user equipment terminal codebook.

(16). The beam training method according to (15), wherein the multiplecombinations between the weight vectors in the user terminal codebookand the weight vectors in the base station terminal codebook comprise:

all combinations between the weight vectors in the user terminalcodebook and the weight vectors in the base station terminal codebook.

(17). The beam training method according to (15), wherein the multiplecombinations between the weight vectors in the user terminal codebookand the weight vectors in the base station terminal codebook comprise:

at least a portion of all the combinations between the weight vectors inthe user terminal codebook and the weight vectors in the base stationterminal codebook.

(18). The beam training method according to (17), wherein the multiplecombinations between the weight vectors in the user terminal codebookand the weight vectors in the base station terminal codebook comprise:combinations between one of the weight vectors in the base stationterminal codebook and all the weight vectors in the user terminalcodebook, and combinations between one of the weight vectors in the userterminal codebook and all the weight vectors in the base stationterminal codebook.

(19). The beam training method according to (18) wherein according tochannel qualities obtained from combinations between one of the weightvectors in the base station terminal codebook and all the weight vectorsin the user terminal codebook, weight vectors to be combined with allthe weight vectors in the base station terminal codebook are selectedfrom the weight vectors in the user terminal codebook.

(20). The beam training method according to (15), wherein in the step ofselecting a corresponding channel quality for each weight vector in thebase station terminal codebook according to the channel qualities toform a first channel quality set, an optimal channel quality is selectedfor each weight vectors in the base station terminal codebook.

(21). The beam training method according to (15), wherein in the step ofselecting a corresponding channel quality for each weight vector in theuser terminal codebook according to the channel qualities to form asecond channel quality set, an optimal channel quality is selected foreach weight vectors in the user terminal codebook.

(22). The beam training method according to (15), further comprising:before performing downlink beam training, sending the reduced userequipment terminal codebook to the user equipment.

(23). The beam training method according to (15), further comprising:sending antenna parameters from the user equipment to the base station.

(24). The beam training method according to (23), wherein the antennaparameters comprise an antenna type and/or antenna spacing.

(25). The beam training method according to (23), wherein the basestation calculates antenna response vectors of the user equipment basedon the antenna parameters.

(26). The beam training method according to (15), further comprising:correcting the reduced base station terminal codebook.

(27). The beam training method according to (26), wherein the step ofcorrecting the reduced base station terminal codebook comprises:

for each weight vector in the reduced base station terminal codebook,calculating a horizontal arrival angle and a vertical arrival angle thatminimize a distance between the weight vector and each base stationterminal antenna response vector of an uplink channel;

obtaining a first antenna response vector of the base station terminalof a downlink channel corresponding to the calculated horizontal arrivalangle and vertical arrival angle;

selecting, from the base station terminal codebook, a weight vectorhaving the smallest distance from the first antenna response vector as acorrected weight vector.

(28). The beam training method according to (15), further comprising:correcting the reduced user terminal codebook.

(29). The beam training method according to (28), wherein the step ofcorrecting the reduced user terminal codebook comprises:

for each weight vector in the reduced user terminal codebook,calculating a horizontal arrival angle and a vertical arrival angle thatminimize a distance between the weight vector and each user equipmentterminal antenna response vector of an uplink channel:

obtaining a second antenna response vector of the user equipmentterminal of a downlink channel corresponding to the calculatedhorizontal arrival angle and vertical arrival angle;

selecting, from the user equipment terminal codebook, a weight vectorhaving the smallest distance from the second antenna response vector asa corrected weight vector.

(30). The beam training method according to (27) or (29), wherein thehorizontal arrival angle and the vertical arrival angle are discretizedthrough sampling.

(31). The beam training method according to (30), wherein the number ofsampling points of the horizontal arrival angle is equal to an integermultiple of the number of corresponding antennas in the horizontaldirection, and the number of sampling points of the vertical arrivalangle is equal to an integer multiple of the number of correspondingantennas in the vertical direction.

(32). A base station for frequency division duplex (FDD) millimeter wavecommunication, comprising a processor, the processor configured to:

receiving an uplink training sequence sent by a user equipment accordingto a user terminal codebook;

calculating channel qualities under multiple combinations between weightvectors in the user terminal codebook and weight vectors in a basestation terminal codebook;

selecting a corresponding channel quality for each weight vector in thebase station terminal codebook according to the channel qualities toform a first channel quality set;

selecting a corresponding channel quality for each weight vector in theuser terminal codebook according to the channel qualities to form asecond channel quality set;

selecting a first predetermined number of channel qualities from thefirst channel quality set and generating a reduced base station terminalcodebook based on the weight vectors corresponding to the firstpredetermined number of channel qualities;

selecting a second predetermined number of channel qualities from thesecond channel quality set and generating a reduced user equipmentterminal codebook based on the weight vectors corresponding to thesecond predetermined number of channel qualities; and

performing downlink beam training using the reduced base stationterminal codebook and the reduced user equipment terminal codebook.

(33). A base station for Frequency Division Duplex (FDD) millimeter wavecommunication, comprising:

a receiving unit for receiving an uplink training sequence sent by auser equipment according to a user terminal codebook;

a calculation unit for calculating channel qualities under multiplecombinations between weight vectors in the user terminal codebook andweight vectors in a base station terminal codebook;

a first set generation unit for selecting a corresponding channelquality for each weight vector in the base station terminal codebookaccording to the channel qualities to form a first channel quality set;

a second set generation unit for selecting a corresponding channelquality for each weight vector in the user terminal codebook accordingto the channel qualities to form a second channel quality set;

a first selecting unit for selecting a first predetermined number ofchannel qualities from the first channel quality set;

a second selecting unit for selecting a second predetermined number ofchannel qualities from the second channel quality set;

a first codebook generation unit for generating a reduced base stationterminal codebook based on weight vectors corresponding to the firstpredetermined number of channel qualities;

a second codebook generation unit for generating a reduced userequipment terminal codebook based on weight vectors corresponding to thesecond predetermined number of channel qualities; and

performing downlink beam training using the reduced base stationterminal codebook and the reduced user equipment terminal codebook.

(34). A beam training method for frequency division duplex (FDD)millimeter wave communication, comprising:

sending, by a base station, a downlink training sequence to a userequipment according to a base station terminal codebook;

receiving, by the user equipment, the downlink training sequence andcalculating channel qualities under multiple combinations between weightvectors in a user terminal codebook and weight vectors in the basestation terminal codebook;

selecting a corresponding channel quality for each weight vector in thebase station terminal codebook according to the channel qualities toform a first channel quality set;

selecting a corresponding channel quality for each weight vector in theuser terminal codebook according to the channel qualities to form asecond channel quality set;

selecting a first predetermined number of channel qualities from thefirst channel quality set and generating a reduced base station terminalcodebook based on the weight vectors corresponding to the firstpredetermined number of channel qualities;

selecting a second predetermined number of channel qualities from thesecond channel quality set and generating a reduced user equipmentterminal codebook based on the weight vectors corresponding to thesecond predetermined number of channel qualities; and

performing uplink beam training using the reduced base station terminalcodebook and the reduced user equipment terminal codebook.

(35). The beam training method according to (34), further comprising:correcting the reduced base station terminal codebook.

(36). The beam training method according to (35), wherein the step ofcorrecting the reduced base station terminal codebook comprises:

for each weight vector in the reduced base station terminal codebook,calculating a horizontal arrival angle and a vertical arrival angle thatminimize a distance between the weight vector and each base stationterminal antenna response vector of a downlink channel;

obtaining a third antenna response vector of the base station terminalof an uplink channel corresponding to the calculated horizontal arrivalangle and vertical arrival angle;

selecting, from the base station terminal codebook, a weight vectorhaving the smallest distance from the third antenna response vector as acorrected weight vector.

(37). The beam training method according to (34), further comprising:correcting the reduced user terminal codebook.

(38). The beam training method according to (34), wherein the step ofcorrecting the reduced user terminal codebook comprises:

for each weight vector in the reduced user terminal codebook,calculating a horizontal arrival angle and a vertical arrival angle thatminimize a distance between the weight vector and each user equipmentterminal antenna response vector of a downlink channel;

obtaining a fourth antenna response vector of the user equipmentterminal of an uplink channel corresponding to the calculated horizontalarrival angle and vertical arrival angle;

selecting, from the user equipment terminal analog codebook, a weightvector having the smallest distance from the fourth antenna responsevector as a corrected weight vector.

(39). A user equipment for frequency division duplex (FDD) millimeterwave communication, comprising a processor, wherein the processor isconfigured to:

receiving a downlink training sequence sent by a base station accordingto a base station terminal codebook;

calculating channel qualities under multiple combinations between weightvectors in a user terminal codebook and weight vectors in the basestation terminal codebook;

selecting a corresponding channel quality for each weight vector in thebase station terminal codebook according to the channel qualities toform a first channel quality set;

selecting a corresponding channel quality for each weight vector in theuser terminal codebook according to the channel qualities to form asecond channel quality set;

selecting a first predetermined number of channel qualities from thefirst channel quality set and generating a reduced base station terminalcodebook based on the weight vectors corresponding to the firstpredetermined number of channel qualities;

selecting a second predetermined number of channel qualities from thesecond channel quality set and generating a reduced user equipmentterminal codebook based on the weight vectors corresponding to thesecond predetermined number of channel qualities; and

performing uplink beam training using the reduced base station terminalcodebook and the reduced user equipment terminal codebook.

(40). A user equipment for frequency division duplex (FDD) millimeterwave communication, comprising:

a receiving unit for receiving a downlink training sequence sent by abase station according to a base station terminal codebook;

a calculation unit for calculating channel qualities under multiplecombinations between weight vectors in the user terminal codebook andweight vectors in a base station terminal codebook;

a first set generation unit for selecting a corresponding channelquality for each weight vector in the base station terminal codebookaccording to the channel qualities to form a first channel quality set;

a second set generation unit for selecting a corresponding channelquality for each weight vector in the user terminal codebook accordingto the channel qualities to form a second channel quality set;

a first selecting unit for selecting a first predetermined number ofchannel qualities from the first channel quality set;

a second selecting unit for selecting a second predetermined number ofchannel qualities from the second channel quality set;

a first codebook generation unit for generating a reduced base stationterminal codebook based on weight vectors corresponding to the firstpredetermined number of channel qualities;

a second codebook generation unit for generating a reduced userequipment terminal codebook based on weight vectors corresponding to thesecond predetermined number of channel qualities; and

performing uplink beam training using the reduced base station terminalcodebook and the reduced user equipment terminal codebook.

(41). A communication system, comprising a user equipment and a basestation according to (32) or (33).

(42). A communication system, comprising a base station and a userequipment according to (39) or (40).

(43). A beam training method for frequency division duplex (FDD)millimeter wave communication, comprising:

sending, by a second communication device, a training sequence to afirst communication device according to a second device terminalcodebook;

receiving, by the first communication device, the training sequence andcalculating channel qualities under multiple combinations between weightvectors in a first communication device terminal codebook and weightvectors in the second communication device terminal codebook;

selecting a corresponding channel quality for each weight vector in thefirst communication device terminal codebook according to the channelqualities to form a first channel quality set;

selecting a corresponding channel quality for each weight vector in thesecond communication device terminal codebook according to the channelqualities to form a second channel quality set;

selecting a first predetermined number of channel qualities from thefirst channel quality set and generating a reduced first communicationdevice terminal codebook based on the weight vectors corresponding tothe first predetermined number of channel qualities;

selecting a second predetermined number of channel qualities from thesecond channel quality set and generating a reduced second communicationdevice terminal codebook based on the weight vectors corresponding tothe second predetermined number of channel qualities; and

performing beam training for sending information from the firstcommunication device to the second communication device by using thereduced first communication device terminal codebook and the reducedsecond communication device terminal codebook.

(44). A beam training method for frequency division duplex (FDD)millimeter wave communication, comprising:

sending, by a second communication device, a training sequence to afirst communication device according to a second device terminalcodebook;

receiving, by the first communication device, the training sequence andcalculating channel qualities under multiple combinations between weightvectors in a first communication device terminal codebook and weightvectors in the second communication device terminal codebook;

selecting a corresponding channel quality for each weight vector in thefirst communication device terminal codebook according to the channelqualities to form a first channel quality set;

selecting a corresponding channel quality for each weight vector in thesecond communication device terminal codebook according to the channelqualities to form a second channel quality set;

selecting a first predetermined number of channel qualities from thefirst channel quality set and generating a reduced first communicationdevice terminal codebook based on the weight vectors corresponding tothe first predetermined number of channel qualities;

selecting a second predetermined number of channel qualities from thesecond channel quality set and generating a reduced second communicationdevice terminal codebook based on the weight vectors corresponding tothe second predetermined number of channel qualities; and

performing beam training for sending information from the firstcommunication device to the second communication device by using thereduced first communication device terminal codebook and the reducedsecond communication device terminal codebook.

(45). The method according to (44), further comprising:

selecting a corresponding channel quality for each weight vector in thesecond communication device terminal codebook according to the channelqualities to form a second channel quality set;

selecting a second predetermined number of channel qualities from thesecond channel quality set and generating a reduced second communicationdevice terminal codebook based on the weight vectors corresponding tothe second predetermined number of channel qualities; and

performing beam training for sending information from the firstcommunication device to the second communication device by using thereduced first communication device terminal codebook and the reducedsecond communication device terminal codebook.

(46). A beam management method used in a frequency division duplex (FDD)communication system, comprising:

performing beam measurement on a set of transmission beams from asubject communication node based on a set of reception beams;

based on beam measurement results, performing selection on receptionbeams to determine a subset of the set of reception beams; and

transmitting backward beams to the subject communication node forbackward beam measurement based on beam directions corresponding to thesubset of the set of reception beams.

(47). The method according to (46), further comprising: based on beammeasurement results, performing selection on transmission beams todetermine a subset of the set of transmission beams, and indicatinginformation of the subset of the set of transmission beams to thesubject communication node, so that the subject communication nodereceives the backward beams based on beam directions corresponding tothe subset of the set of transmission beams.

(48) The method according to (46), wherein a number of the backwardbeams is equal to a number of reception beams included in the subset ofthe-set of reception beams.

(49) An electronic device, comprising a processing circuit configured toperform the method of any one of (46) to (48).

Hereto, the beam training method and the electronic device used for thebase station and the user equipment according to the present inventionhave been described in detail. In order to avoid obscuring the conceptsof the present invention, some details known in the art are notdescribed. Based on the above description, those skilled in the art canunderstand how to implement the technical solutions disclosed herein.

The method and system of the present invention may be implemented inmany ways. For example, the method and system of the present inventionmay be implemented by software, hardware, firmware, or any combinationof software, hardware, and firmware. The above sequence of steps of themethod is merely for illustration, and the steps of the method of thepresent invention are not limited to the above order which is describedspecifically unless otherwise specified. In addition, in someembodiments, the present invention may also be implemented as programsrecorded in a recording medium, which include machine-readableinstructions for implementing the method according to the presentinvention. Thus, the present invention also covers a recording mediumstoring programs for executing the method according to the presentinvention.

Although some specific embodiments of the present invention have beendescribed in detail by way of example, those skilled in the art shouldunderstand that the above examples are only for the purpose ofillustration and are not intended to limit the scope of the presentinvention. It should be understood by those skilled in the art that theabove embodiments may be modified without departing from the scope andspirit of the present invention. The scope of the present invention isdefined by the following claims.

What is claimed is:
 1. An electronic device for a user equipment in awireless communication system, comprising: a processing circuitconfigured to: receive, from a base station, channel state informationreference signal with a set of reception filters; perform measurement ofthe channel state information reference signal; select, from the set ofreception filters, one or more particular reception filterscorresponding to respective measurement results that satisfy a firstpredetermined condition; and signal, from the user equipment to the basestation, sounding reference signal with one or more particulartransmission filters, wherein the one or more particular transmissionfilters and one or more particular reception filters are reciprocalrespectively.
 2. The electronic device according to claim 1, wherein theprocessing circuit is further configured to receive, from the basestation, configuration information indicating the reciprocalrelationship between the one or more particular transmission filters andone or more particular reception filters.
 3. The electronic deviceaccording to claim 1, wherein the set of reception filters indicateantenna arrival angles.
 4. The electronic device according to claim 1,wherein the one or more particular reception filters include a downlinkchannel matrix that is reciprocal to an uplink channel matrix of the oneor more particular transmission filters.
 5. The electronic deviceaccording to claim 1, wherein the set of reception filters correspondsto a weight vector, and each weight vector is used to configure phasevalues for phase shifters of a set of phase shifters connected to aradio frequency link, and is used to transmit antenna beams in specificspatial directions.
 6. The electronic device according to claim 1,wherein the processing circuit is further configured to: generate anexhaustive search by detecting all possible combinations between weightvectors of the user equipment and weight vectors of the base station;measure channel quality between the weight vectors of all possiblecombinations; and select from the measured channel qualities, as thefirst predetermined condition an optimal set of weight vectors to bedetermined to be the set of reception filters.
 7. The electronic deviceaccording to claim 1, wherein the wireless communication system is afrequency division duplex system; wherein the one or more particulartransmission filters and one or more particular reception filters arereciprocal respectively based on reciprocity of arrival angles in uplinkand downlink channels in the frequency division duplex system; and theprocessing circuit is further configured to: obtain information frombeam training in the uplink channel to facilitate beam training in thedownlink channel.
 8. The electronic device according to claim 1, furthercomprising: storage circuitry configured to store an analog codebook forthe base station, the analog codebook comprising a plurality of sets ofsecond configuration parameters for a set of phase shifters of the basestation; and channel estimation circuitry configured to estimate channelquality of an uplink based on the stored analog codebook and thesounding reference signal.
 9. An electronic device for a base station ina wireless communication system, comprising: a processing circuitconfigured to: receive, from a user equipment, sounding reference signalwith a set of reception filters; perform measurement of the soundingreference signal; select, from the set of reception filters, one or moreparticular reception filters; and transmit to the user equipment withone or more particular transmission filters, wherein the one or moreparticular transmission filters and one or more particular receptionfilters are reciprocal respectively.
 10. The electronic device accordingto claim 9, wherein the processing circuit is further configured tosend, to the user equipment, a notification of the reciprocalrelationship between the one or more particular transmission filters andone or more particular reception filters.
 11. The electronic deviceaccording to claim 9, further comprising: a storage device configured tostore an analog codebook for the user equipment, the analog codebookcomprising a plurality of sets of second configuration parameters for aset of phase shifters of the user equipment.
 12. The electronic deviceaccording to claim 9, wherein the processing circuit is furtherconfigured to: receive, from the user equipment, an optimal set ofweight vectors determined to be the set of reception filters.
 13. Theelectronic device according to claim 12, wherein the processing circuitis further configured to: transmit, to the user equipment, a pilotsignal for each of the weight vectors of the base station to estimateeach of the measured channel qualities.
 14. The electronic deviceaccording to claim 13, wherein the processing circuit is furtherconfigured to: receive, from the user equipment, an index of he optimalset of weight vectors.
 15. The electronic device according to claim 9,further comprising a hybrid precoding architecture including: a digitalprecoder configured to obtain a plurality of data streams as input andto perform digital precoding on each of the plurality of data streamsand to process the plurality of data streams by forming respective radiofrequency links each corresponding to a plurality of terminals of a typeas the user equipment; and an analog phase-shifting network connectingto the radio frequency links.
 16. The electronic device according toclaim 9, further comprising a hybrid precoding architecture including: adigital precoder configured to obtain a plurality of data streams asinput and to perform digital precoding on each of the plurality of datastreams and to process the plurality of data streams by formingrespective radio frequency links each corresponding to a plurality ofterminals of a type as the user equipment; and an analog phase-shiftingnetwork connecting to the radio frequency links; wherein the analogphase-shifting network is a full connection phase-shifting network. 17.The electronic device according to claim 9, further comprising a hybridprecoding architecture including: a digital precoder configured toobtain a plurality of data streams as input and to perform digitalpreceding on each of the plurality of data streams and to process theplurality of data streams by forming respective radio frequency linkseach corresponding to a plurality of terminals of a type as the userequipment; and an analog phase-shifting network connecting to the radiofrequency links; wherein the analog phase-shifting network is asub-connection phase-shifting network.